This invention relates to joining diamond bodies.
It is possible to synthesise diamond from the gas phase. This method is known as chemical vapour deposition (CVD) and the diamond produced is known as CVD diamond. The process generally involves providing a mixture of hydrogen gas and a suitable gaseous carbon compound such as a hydrocarbon, applying sufficient energy to that gas to dissociate the hydrogen into atomic hydrogen and the gas into active carbon ions, atoms or CH radicals and allowing such active species to deposit on a substrate to form diamond. Dissociation of the gases can take place by a variety of methods.
One such method is the use of a hot filament. In this method, the gas temperature at the filament is about 2000.degree. C. and the substrate on which diamond growth occurs is at 800.degree. to 1100.degree. C.
A second commonly used method is a plasma assisted method. The hydrogen and gaseous carbon compound enter a plasma region, which may be microwave, RF or DC plasma, where they are excited to their reactive states. They diffuse in this state to a substrate. The substrate is heated by the plasma.
Yet a further method of exciting the hydrogen/gaseous carbon compound mixture is with the use of a plasma jet. One such method is described in EP 0286306 which involves effecting an arc discharge while feeding a discharge gas between an anode and a cathode of a thermal plasma chemical vapour deposition device, activating or producing radicals from a gaseous carbon compound by feeding the gaseous compound to a generated plasma jet and permitting the plasma jet containing the radicals to impinge on a substrate thereby to form diamond on the substrate.